2013 Annual Science Report

University of Wisconsin Reporting  |  SEP 2012 – AUG 2013

Executive Summary

Our activities in Year 1 were focused on five themes, all of which broadly fall within the team’s efforts in pushing new approaches to “life detection”: i) Analog settings and the biomolecules of life; ii) Experimental studies of paleoenvironmental and biological proxies; iii) Hadean, Archean, and Proterozoic environments and biosphere; iv) Building the Astrobiology infrastructure; and v) Education and public outreach.

Theme 1: Analog Settings and the Biomolecules of Life

Six projects were pursued under the theme of analog setting and biomolecules in Year 1. In Project 1A: Detection of Biosignatures in Extreme Environments and Analogs for Mars, Co-I Max Coleman continued prior work on characterizing the isotopic equilibria between sulfite and water, which is relevant to understanding part of the microbial sulfate reduction system, as well as sulfite oxidation; these isotopic effects may potentially help understand sulfur redox cycling on early Mars. In ... Continue reading.

Field Sites
31 Institutions
16 Project Reports
24 Publications
13 Field Sites

Project Reports

  • Project 1C: Compositional and Structural Variations in Dolomite and Ca-Bearing Magnesite From Modern and Ancient Carbonate Sediments

    Low-temperature Ca-Mg carbonates that have a wide range of chemical variation (from high-Mg calcite to Ca-bearing magnesite) may be used as a biosignature. Certain polysaccharides can inhibit aragonite precipitation and promote Ca-Mg-carbonate crystallization. Experiments indicate that ancient low-temperature, non-stoichiometry dolomite with the observed nano-precipitates of Ca-rich phases may be used as a biosignature.

  • Project 1F: Organics Exposure in Orbit (OREOcube): A Next-Generation Space Exposure Platform

    The OREOcube (ORganics Exposure in Orbit cube satellite) experiment on the International Space Station (ISS) investigates the effects of solar and cosmic radiation on organic thin films. By depositing organic samples onto inorganic substrates, structural changes and photo-modulated organic-inorganic interactions are examined to study the role that solid mineral surfaces play in the photo-chemical evolution, transport, and distribution of organics. The results of these experiments in low Earth orbit (LEO) allow extrapolation to different solar system and interstellar/interplanetary environments. Organic molecules appropriate for study in thin-film form include biomarkers such as amino acids and nucleobases, as well as polyaromatic hydrocarbons (PAHs), redox molecules, and organosulfur compounds. Inorganic substrates include silicates, metal oxides, iron sulfides, nano-phase iron, and iron-nickel alloys. By measuring changes in the UV-vis-NIR spectra of samples as a function of time in situ on the ISS, OREOcube will provide data sets that capture critical kinetic and mechanistic details of sample reactions that cannot be obtained with current exposure facilities in LEO. Combining in situ, real-time kinetic measurements with post-flight sample analysis will provide time-course studies, as well as in-depth chemical analysis, enabling us to characterize and model the chemistry of organic species associated with mineral surfaces in the astrobiological context.

    ROADMAP OBJECTIVES: 3.1 5.3 7.1
  • Project 2A: Magnesium Isotope Fractionation Between Brucite [Mg(OH)2] and Mg Aqueous Species

    Recognition of clay minerals on Noachian martian terranes provides important information on the habitability of early Mars. Magnesium isotopic studies can aid in constraining the paleoenvironmental conditions of these clay deposits. Our goal is to conduct Mg isotope exchange experiments between clay minerals and aqueous Mg solutions to better understand how the formation of clay minerals can produce Mg isotope variability. In Mg-bearing phyllosilicates, octahedrally coordinated Mg2+ cations occur in a sheeted structure that is the same as brucite. Determination of Mg isotope fractionation between brucite and aqueous solution, therefore, may provide insight into the origin of Mg isotope variations during weathering and alteration of silicate rocks. Our results document the distinct Mg isotope signals produced by weathering in the presence of organic ligands, raising the possibility that abiotic weathering may be distinguished from biologically-catalyzed weathering using stable Mg isotopes.

    ROADMAP OBJECTIVES: 1.1 2.1 7.1 7.2
  • Project 4A: Better, Faster, Smaller Fe Isotope Analysis on Iron Oxides and Sulfides by Femtosecond Laser Ablation: Aerosol Characterization and the Influence of Ablation Cells

    New methods are being developed for in situ stable isotope analysis that increase the precision and/or decrease the volume sampled during the analysis. These improvements allow one to identify isotopic anomalies with increasing spatial resolution. We have focused on improving the ablation cell and mass spectrometer electronics to increase the spatial resolution of Fe isotope studies on iron oxides and sulfides whilst maintaining an external precision of +0.2 ‰ in 56Fe/54Fe using femtosecond Laser Ablation (fs-LA) with isotopic analysis by MC-ICP-MS (Micromass “IsoProbe”). These improvements have allowed us to decrease the volume needed for an Fe isotope analysis to ~600μm3 with an external precision of 0.2 ‰ in 56Fe/54Fe (for a typical analysis the laser beam is rastered over an area of 20 by 15 μm). Compared to previous LA Fe isotope studies the volume used for an analysis in an order of magnitude smaller and is similar to Fe isotope studies that have been done by ion microprobe.

    ROADMAP OBJECTIVES: 1.1 2.1 7.1 7.2
  • Project 2B: Origin of Carbonates: Environmental Proxies and Formation Pathways

    Magnesium isotopes can provide insights into past environmental conditions including formation temperatures and sources of Mg for carbonates, including dolomite, which is a common sedimentary carbonate of the geologic rock record. For Mg isotopes to be a useful proxy, the factors that control isotope fractionation during formation of carbonates must be known. Previous experimental studies have provided conflicting results on potential kinetics effects during the inorganic synthesis of Mg-calcite from solution. To resolve these differences, a matrix of 34 laboratory experiments were conducted to independently determine the effects of temperature, precipitation kinetics, and solution composition (e.g.,pCO2, aqueous Mg/Ca ratio) on Mg- isotope fractionation in the Mg-calcite-aqueous Mg system. Preliminary results suggest that factors in addition to precipitation rate (e.g., aqueous Mg/Ca ratio, pCO2) may play a role in the fractionation of Mg isotopes in the Mg-calcite-aqueous Mg system.

  • Project 1D: Potential for Microbial Iron Reduction in Chocolate Pots Hot Springs, Yellowstone National Park

    Iron biogeochemical cycling in circumneutral pH hot spring systems is an increasingly important astrobiological target, given recent discoveries on Mars by Curiosity. This study explored the potential for microbial reduction of ferric iron Fe(III) in the warm (ca. 40-60 C), circumneutral pH (ca. 6.0-6.5) Chocolate Pots (CP) hot springs in Yellowstone National Park. Endogenous microbial communities were able to reduce native CP Fe(III) oxides, as documented in most probable number (MPN) enumerations and ongoing enrichment culture studies. Microbial communities in the enrichments have been analyzed by high-throughput pyrosequencing of 16S rRNA gene amplicons. The sequencing revealed an abundance of the well-known Fe(III)-reducing bacterial species, Geobacter metallireducens, as well several other novel organisms with the potential to contribute to Fe(III) reduction. A shotgun metagenomic (paired-end Illumina sequencing) analysis of the enrichment cultures is in progress to explore the identity and function of G. metallireducens as well as other less well-characterized organisms in the cultures. Of particular interest are the likely presence of thermotolerance genes in the G. metallireducens metagenome, as well as outer membrane cytochrome genes that may be indicative of other Fe(III)-reducing organisms and provide evidence for pathways of electron flow in these cultures.

    ROADMAP OBJECTIVES: 2.1 5.1 6.1 7.1
  • Project 1E: Metagenomic Analysis of Novel Chemolithoautotrophic Bacterial Cultures

    Metagenomic sequence information was obtained from two chemolithoautotrophic bacterial cultures: (1) an iron-oxidizing, nitrate-reducing culture that is capable of growth with either soluble or insoluble, mineral-bound (biotite, smectite) Fe(II) as the sole energy source; and (2) an aerobic iron/sulfur-oxidizing culture that grows with insoluble framboidal pyrite as the sole energy source. Both of these cultures carry-out novel neutral-pH lithotrophic microbial pathways, the discovery of which broadens our view of potential Fe/S based life on Earth (past and present) and other rocky planets. We hypothesize that genetic components of Fe/S oxidation identified in the metagenome of the cultures will bear resemblance to analogous components to be identified in other iron-oxidizing pure cultures being sequenced at JGI, together with existing published and unpublished information from other chemolithoautotrophic microorganisms. Identification of such genetic systems will enable comparative genomic analysis of mechanisms of extracellular phyllosilicate Fe/S redox metabolism, and facilitate development of techniques to detect the presence and expression of genes associated with chemolithotrophic Fe/S metabolism in various terrestrial environments.

    ROADMAP OBJECTIVES: 3.2 5.1 5.3 6.2
  • Project 1A: Detection of Biosignatures in Extreme Environments and Analogs for Mars

    Sulfate, a chemical form containing sulfur and oxygen, is present in ocean water and is a component of minerals on Earth and on Mars, created by evaporation of such water. We have been measuring variations in the relative abundances of naturally-occurring, non-radioactive oxygen isotopes in sulfate to indicate what processes were involved in sulfate formation: for example microbes gaining energy from sulfide or via a non-biological route. A precursor chemical in the formation of sulfate is sulfite, containing sulfur and just a little less oxygen. We have shown recently that the oxidation of sulfite (adding more oxygen), governs the oxygen isotope composition of sulfate. This work will be of significant importance in helping us to understand conditions of formation of ancient minerals.

  • Project 3A: Banded Iron Formation Deposition Across the Archean-Proterozoic Boundary

    Prior to widespread oxygenic photosynthesis, reduced iron, Fe(II), was the dominant form of soluble iron in surface environments on the early Earth, and likely Mars. On Earth, extensive iron deposits, Banded Iron Formations (BIFs), which currently supply the majority of the iron used in our society, largely formed prior to the Great Oxidation Event of ~2.4 Ga age, and yet contain substantial quantities of oxidized iron, Fe(III). The pathways by which these different oxidation states arose remains unclear. In addition, the chemical and isotopic compositions of BIFs have been used as proxies for ancient seawater or paleoenvironments. In competition with this proposal, however, has been use of BIFs as a tracer of microbial iron cycling. To test the use of BIFs as ambient paleoenvironmental proxies or proxies of microbial process, BIFs from South Africa and Australia were examined from the micron scale to the 100’s of meter scales. We find that BIFs tend to record specific pathways of oxidation of Fe(II), as well as reduction of Fe(III), and extensive post-depositional changes, and it may be quite difficult to infer ambient paleoenvironmental conditions form such deposits.

    ROADMAP OBJECTIVES: 2.1 4.1 5.2 6.1 7.1 7.2
  • Project 1B: The Extraction of Spiked Amino Acids From a Set of (Clay-Rich) Minerals

    In the search for life on Earth and beyond, scientists scan for molecular organic compounds indicative for life, called biomarkers. Amino acids are among the most widespread biomolecules on Earth and play an important role in terrestrial biology by being, among other things, the building blocks of proteins. Thus, they are also selected as priority biomarkers for future life detection missions on Mars. Efficient extraction and detection of these biomarkers is of great importance. It is well known that amino acids degrade over time. This is caused by enzymatic and oxidative processes, as well as by UV- and ionizing radiation from the Sun, unless they are shielded from these influences. Mineral substrates, in particular clays such as montmorillonite, adsorb organic compounds efficiently and may have played a central role in the evolution of life. Rock formations, built up from clay-rich minerals, are therefore a priority target for life detection strategies. However, strong adsorption of amino acids by clay-rich minerals in turn inhibits extraction, resulting in low recovery rates. The aim of this study was to determine the extraction efficiency of amino acids from several distinctive (clay-rich) minerals. This was achieved by spiking minerals with amino acid solutions. After spiking, the samples were subjected to an extraction method. The abundances of recovered amino acids were then compared to the content of the original spiking solutions. Before the extraction experiments were conducted, several parameters were determined that could influence extraction rates (particle size, swelling capacities of the minerals, and carbon/nitrogen content). In this report we discuss preliminary results of adsorption properties of four amino acids: Arginine, Aspartic acid, Glutamic acid and Serine.

  • Project 2C: Calibrating the 13C-18O (“clumped”) Isotope Temperature Scale

    Determining paleotemperatures in ancient fluid-mineral systems is key to determining ancient habitability. Stable oxygen isotope studies of carbonates have long used changes in 18O/16O ratios to infer the temperature from which carbonate precipitated, using a laboratory-calibrated temperature conversion, but this requires knowledge of the 18O/16O ratios of the fluid. This is often not known. A relatively new approach is to use the non-random variations in rare C and O isotopes, specifically the preferential enhancement of 13C-18O bonds, which has been shown to be related to temperature and independent of the fluid isotopic composition. Experimental calibrations, however, have been inconsistent, and goal of this project is to reconcile these discrepancies.

    ROADMAP OBJECTIVES: 2.1 4.1 7.1 7.2
  • Project 2D: Catalytic Roles of Microbes in Dolomite Crystallization in a Modern Hypersaline Lake

    A key question is if the presence of Mg-bearing carbonates, such as dolomite or proto-dolomite, by itself, represents a biosignature. This proposal is based on the observation that inorganic precipitation of Mg-bearing carbonates is difficult in laboratory settings, possibly reflecting the high Mg dehydration energies in aqueous solutions. New work shows that microbial extracellular polymeric substances substance (EPS) from halophylic archaea from a hypersaline lake can catalyze disordered dolomite precipitation at low-temperature. Mg-rich dolomite can form at 40 degree C. No dolomite precipitates from solutions without the biomass. Low-temperature dolomite with wide range of compositions may therefore be used as a biosignature.

    ROADMAP OBJECTIVES: 6.1 7.1 7.2
  • Project 2E: Carbonate-Associated Sulfate (CAS) as a Tracer of Ancient Microbial Ecosystems

    The iron carbonate mineral, siderite, in sedimentary rocks is usually formed by microbial processes. The presence of small amounts of metals other than iron, and the stable isotope compositions of carbon and oxygen, give information on the details of the microbial ecosystem that produced it and its environment of formation. In particular, if associated with iron sulfide (pyrite), it indicates the former presence of at least two different microbial metabolic processes. In addition, carbonate minerals can contain trace amounts of the chemical compound sulfate, in which the isotopic compositions of sulfur and oxygen reveal further details of the microbial process if that sulfate can be released unaltered from the minerals. Our first challenge in this project has been to develop a method for releasing the original, preserved sulfate without contaminating it with somewhat similar material produced from oxidation of pyrite as an artifact of the preparation method.

    ROADMAP OBJECTIVES: 5.2 6.1 7.1
  • Project 3D: Microfossil Insights Into Proterozoic Microbial Ecology

    In a study of the chert-permineralized 1.8 Ga Duck Creek Dolomite, and underlying units, Western Australia, Schopf found that in sequences of 2.3 to 1.8 Ga age that indicate little environmental change, there has been no evolution of the form, function, or metabolic requirements of its biotic components. In a second study of sulfur-cycling bacteria from the 775 Ma chert-permineralized Bambui Group of Brazil, Schopf showed that pyritized microbes of this age were anaerobic sulfur-cyclers. This work, in addition to previous studies, forms the basis for ongoing studies of the biotic response to the Great Oxidation Event.

    ROADMAP OBJECTIVES: 4.1 5.1 5.2 6.1 7.2
  • Project 3C: Carbon Isotope Analysis of Proterozoic Microfossils

    We have developed procedures for accurate in situ analysis of carbon isotope ratios by SIMS for individual Precambrian microfossils of unquestioned biogenicity. Data for three Proterozoic localities show a consistent fractionation of 19 per mil between organic matter and coexisting carbonates, in spite of over 6 per mil variability from rock to rock, consistent with fractionations seen for modern cyanobacteria. In one sample, a phytoplanktonic protistan acritarch, found within the same mm-scale domains, are 6 per mil more fractionated, consistent with photosynthetic eukaryotes. These findings show for the first time the possibility of using in situ isotopic microanalysis of fossil microbial mats and ancient sediments in order to distinguish metabolic fingerprints within complex microbial ecosystems and consortia.

    ROADMAP OBJECTIVES: 2.1 4.1 4.2 5.2 7.2
  • Project 3B: Carbon Isotope Analysis of Archean Microfossils

    We have completed a study of petrography, Raman microspectroscopy, and in situ analyses of carbon isotope and H/C ratios using secondary ion mass spectrometry (SIMS) of diverse organic microstructures, including possible microfossils. This work has focussed on two localities of the 3.4-billion-year-old Strelley Pool Formation (Western Australia). For the first time, we show that the wide range of carbon isotope ratios recorded at the micrometer scale correlates with specific types of texture for organic matter (OM), arguing against abiotic processes to produce the textural and isotopic relations. These results support the biogenicity of OM in the Strelley Pool Formation.

    ROADMAP OBJECTIVES: 1.1 2.1 4.1 4.2 5.2 6.2 7.2